For centuries, the energy of the wind has been harnessed by windmills or other wind capturing devices to perform work. In more recent times, wind has been used to drive generators for the production of electricity. Wind powered generators generally fall into one of two classes: either a propeller or turbine type having a horizontal axis, or a vertical axis type having blades or air foils. Generators having a horizontal axis of rotation are probably the most common because, in the past, they have been easier and cheaper to construct. However, windmills having a horizontal axis of rotation are less desirable for several reasons. First, their efficiency is generally fairly low, since they are able to capture only a portion of the air flowing therethrough, and thus are able to extract only a portion of the energy contained in the wind. Secondly, when wind speeds are very high, the end tips of the blades may reach high velocities, thus putting a severe strain on the blade itself. If a larger blade is provided to capture a greater portion of the energy of the air flow, the speed reached by the end tips of the blades increases, thus increasing the stresses on the blades, thereby requiring larger and heavier blades, which further reduce the efficiency of the generator. Thirdly, a yaw control is required to make certain that the blades continually face into the wind. The provision of a yaw control increases the complexity of the generator and reduces its efficiency. Examples of such generators having horizontal axes are found in U.S. Pat. Nos. 3,883,750; 3,942,026; 4,039,848; 3,944,839; 2,388,377; and 2,363,827.
Many difficulties have been encountered with generators having a vertical axis of rotation, and these difficulties have prevented them from being commonly used. The primary difficulty concerns the positioning of the airfoils or blades so that they extract an optimal amount of energy from the wind. Ideally, the airfoils should face the wind when it is desired to give the generator a push, and they should be parallel to the wind flow at other times so as not to impede the rotation of the generator. Also, problems have been encountered in controlling the speed of rotation of such generators. A common solution to this problem is to rotate the individual blades as the entire blade assembly is rotated to position the blades at the proper angle of attack with respect to the wind. Many devices utilize cables, linkages or intricate gearing to maintain the blades at the proper attitude. Examples of such devices are shown in U.S. Pat. Nos. 3,902,072; 2,542,522; 3,793,530; 4,039,848; and 3,743,848. In U.S. Pat. Nos. 3,730,643 and 4,129,787 each blade or sail is pivoted by a servo-motor which responds to changes in the orientation of the blade or sail with respect to the wind. The use of servo-motors draws energy from the system and renders it inefficient, while each of the above-described apparatuses is subject to breakdown because of the intricate gearing involved. Other patents provide other means for positioning the airfoils or blades that do not require an intricate mechanical apparatus, but such devices are not highly efficient. In U.S. Pat. No. 3,995,170, vanes formed of rigged sails fold onto themselves or open up depending upon their orientation to the wind, while U.S. Pat. No. 4,048,947 shows freely rotatable aerodynamic blades balanced by counter weights. Some generators, such as those found in U.S. Pat. Nos. 4,156,580 and 2,667,589 have fixed blade turbine rotors which use shields to deflect the wind flow.
Although each of the above-referenced patents discloses a device for producing electrical power from wind, none of them have been used to produce electrical power on a large scale and on an economically feasible basis, because of the unpredictability of wind and the difficulty in controlling and regulating the output from such a generator. Few of the above generators are capable of withstanding sudden high velocity bursts of wind while still being able to operate smoothly and efficiently at relatively low wind velocities. Furthermore, most of the above generators are not self-starting. Most of the above referenced devices are highly inefficient or complex, as indicated, and some are expensive to manufacture and require continual maintenance. As a result, the electrical energy produced thereby is far more expensive than that which can be obtained from conventional energy sources. Additionally, none of the above generators is particularly aesthetically pleasing, and thus, most detract from the environment in which they are placed.